Preheat the oven to Gas 4, 350°F, 180°C.
Lightly grease and line the base of a 2 lb/900 g loaf tin.
Melt the fat in a saucepan then fry onion for 5 mins or until soft and transparent.
Add flour and cook for a further 2 mins.
Pull pan to one side then gradually stir in milk then cook, stirring throughout, until sauce thickens.
Remove from heat, stir in chopped ground nuts and breadcrumbs.
Season.
Whisk egg whites until stiff.
Fold 2 tbsp egg white into nut mixture, then fold in the remainder.
Place half this mixture into the base of the loaf tin.
Place pine nuts, garlic, basil, Parmesan and 2 egg yolks in a food processor.
Add seasoning, then blend until smooth.
If the mixture is very dry, add remaining egg yolk and process again.
Place on top of nut mixture in the loaf tin, top with remaining nut mixture.
Smooth over top, cover with foil then cook for 2 hrs, or until set and firm to the touch.
Remove from oven, leave to settle for 5 mins, then turn out on to a serving plate, discarding the lining paper.
Garnish and serve with a home-made tomato sauce.